Applicants claim, under 35 U.S.C. xc2xa7 119, the benefit of priority of the filing date of Nov. 21, 2001 of a German patent application, copy attached, Serial Number 101 57 112.7, filed on the aforementioned date, the entire contents of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a control device for controlling the amplitude level of at least one analog scanning signal of a position measuring system. The present invention furthermore relates to a scanning head for the position measuring system, to the position measuring system, and to a method for generating an indication regarding the amplitude level by the control device.
2. Discussion of Related Art
A control of the scanning signals is required particularly when installing the position measuring system. The signal quality, and therefore the accuracy of measurement depends to a considerable extent on the exact adjustment of the scanning head in relation to the scale. To assure a high degree of measuring accuracy in connection with incremental position measuring systems, the scanning signals generated by the scanning head should have a high and identical amplitude, as well as a mutual phase offset of 90xc2x0. The amplitude is essentially determined by the position of the scanning head with respect to the scale, i.e. the distance, rotation and lateral shift of the scanning head perpendicularly with respect to the measuring direction in relation to the scale.
In accordance with WO 90/02956, these parameters of the analog scanning signals can be represented by an oscilloscope. For this purpose, the two scanning signals, which are offset by 90xc2x0 with respect to each other, are conducted to the two channels of a dual-trace oscilloscope, so that a Lissajous shape is generated on the screen. The radius of the Lissajous shape is a measure of the amplitudes, as well as of the phase relationship between both scanning signals.
In accordance with U.S. Pat. No. 5,241,173, the entire contents of which are incorporated herein by reference, the scanning signals are fed to a control device, which compares the amplitude value with a threshold value. If the amplitude value falls below the threshold value, a display device is activated, which is used as an indication that the scanning head has been incorrectly installed in relation to the scale. It is essential here that the control device exclusively outputs information which provides an indication as to whether the scanning head has been correctly or incorrectly installed.
It was already noted that this indication alone is not sufficient for the installation, and that it is advantageous for the user to also receive an indication regarding the signal tendency. To this end it is suggested in EP 1 126 248 A2 to form a deviation signal by comparing the amplitude value with a predetermined nominal value. This deviation signal is used on the one hand for adjusting the scanning signal to a constant amplitude level and, on the other hand it is used as an indication regarding the functional status of the position measuring system. The deviation signal is a measure of the actual scanning distance and is used for setting an optimal scanning distance. The indication provided, for example, in the form of a visual display is proportional to the deviation signal. Changes in the amplitude level in the area of the nominal value have the same effect on the indicator signal as changes in the amplitude level at a greater distance from the nominal value. This makes the adjustment of the position of the scanning head with respect to the scale, as well as the functional control, more difficult.
An object of the present invention is based on disclosing a control device for controlling the amplitude level of at least one scanning signal of a position measuring system, by which an indication can be generated, which permits an improved statement regarding the functional state.
This object is attained by a control device for controlling an amplitude level of an analog scanning signal of a position measuring system, the control device includes a detector that determines an amplitude level of a scanning signal of a position measuring system and generates an amplitude signal as a function of the amplitude level. A deviation determination unit that generates a deviation signal by comparing the amplitude signal with a predetermined nominal signal and an indicator that provides an indication of proper set-up of a scanning head of the position measuring system as a function of the deviation signal. An evaluation arrangement for differently weighting the deviation signal in such a way that with a weak deviation signal, a change in the deviation signal causes a small, or no variation of the indication, and in contrast thereto a larger variation of the indication is caused by a stronger deviation signal.
This object is attained by a scanning head of a position measuring system that has a control unit. The control unit includes a detector that determines an amplitude level of a scanning signal of a position measuring system and generates an amplitude signal as a function of said amplitude level. A deviation determination unit that generates a deviation signal by comparing the amplitude signal with a predetermined nominal signal and an indicator that provides an indication of proper set-up of the scanning head of the position measuring system as a function of the deviation signal. An evaluation arrangement for differently weighting the deviation signal in such a way that with a weak deviation signal, a change in the deviation signal causes a small, or no variation of the indication, and in contrast thereto a larger variation of the indication is caused by a stronger deviation signal.
This object is attained by a position measuring system that includes a scale and a scanning head that scans the scale, wherein the scanning head has a control device. The control device includes a detector that determines an amplitude level of a scanning signal of a position measuring system and generates an amplitude signal as a function of the amplitude level. A deviation determination unit that generates a deviation signal by comparing the amplitude signal with a predetermined nominal signal and an indicator that provides an indication of proper set-up of the scanning head as a function of the deviation signal. An evaluation arrangement for differently weighting the deviation signal in such a way that with a weak deviation signal, a change in the deviation signal causes a small, or no variation of the indication, and in contrast thereto a larger variation of the indication is caused by a stronger deviation signal.
Another object of the present invention is to disclose a method for forming an indication of proper set-up of a scanning head by providing meaningful information.
This object is attained by a method for generating an indication regarding the amplitude level of at least one scanning signal of a position measuring system by determining an amplitude level of at least one scanning signal of a position measuring system, generating an amplitude signal based on the determined amplitude level. Forming a deviation signal by comparing the generated amplitude signal with a predetermined nominal signal and providing an indication of proper set-up of a scanning head of the position measuring system as a function of the deviation signal, wherein with a weak deviation signal, a change in the deviation signal causes a small, or no variation of the indication, and in contrast thereto a larger variation of the indication is caused by a stronger deviation signal.
Details, as well as advantages of the present invention ensue from the following description of exemplary embodiments of the present invention, making reference to the drawings.